1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to an apparatus and method for processing data in a modem for a mobile station used in a communication system.
2. Description of the Related Art
The technology generally used for providing data service to users in the current wireless communication environment is classified into 2.5th generation or 3rd generation cellular mobile communication technology, such as Code Division Multiple Access 2000 1× Evolution Data Optimized (CDMA2000 1×EVDO), General Packet Radio Services (GPRS) together with Universal Mobile Telecommunication Service (UMTS), as well as Wireless Local Area Network (LAN) technology, such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 Wireless LAN and HyperLAN/2.
The 3rd generation mobile communication technology for mainly providing voice service via a circuit-switched network is primarily characterized by providing packet data services in which subscribers can access the Internet in various wireless communication environments.
However, the cellular mobile communication network has a limitation in supporting high-speed packet data service. For example, the CDMA2000 1×EVDO system, which is a synchronous mobile communication system, supports a data rate of at most 2.4 Mbps.
Along with the evolution of the mobile communication technologies, there is an advent of various wireless LAN technologies, such as IEEE 802.16-based wireless LAN, HyperLAN/2 and Bluetooth. Such technologies cannot guarantee mobility on the level of the cellular mobile communication system. However, wireless LAN technologies have replaced the wire communication networks, such as a cable modem and Digital Subscriber Line (xDSL), in hot spot areas such as public place and school, or in the home network environment, making an alternative proposal for providing high-speed data service in the wireless environment.
However, due to the limited mobility, narrow service coverage, radio interference, etc., the use of the wireless LAN in providing high-speed data service causes a limitation in providing public network service to users.
Therefore, many attempts are being made to overcome these limitations. For example, there is active ongoing research regarding the communication technology provided for overcoming the defects of the cellular mobile communication system and the wireless LAN. The available communication technology is presently under standardization and development. The broadband communication system can provide high-speed data service in the indoor/outdoor still/mobile environments using various types of mobile stations. Below is a detailed description of the communication system.
Currently, there is active ongoing research regarding the corresponding system and mobile station (MS) to provide high-speed service in the communication system. However, presently there is no clear specification provided for a modem applied to the MS.
FIG. 1 is a diagram schematically illustrating a data frame format used in a general communication system.
Referring to FIG. 1, there is shown an IEEE 802.16-based data frame format in a general communication system for providing communication service. The data frame used in the communication system distinguishes a downlink (DL) field and an uplink (UL) field in units of time. A Transmit/receive Transition Gap (TTG) forms a guard time in a transition interval from the downlink to the uplink, and a Receive/transmit Transition Gap (RTG) forms a guard time in a transition interval from the uplink to the downlink. In FIG. 1, the horizontal axis represents Orthogonal Frequency Division Multiple Access (OFDMA) symbol numbers, and the vertical axis represents subchannel logical numbers.
In the downlink, a preamble for synchronization acquisition is located in a Kth OFDMA symbol, and broadcast data information commonly received at MSs, such as Frame Control Header (FCH) and DL-MAP, is located in a (K+1)th OFDMA symbol. The FCH, composed of two subchannels, transmits basic information on the subchannel concerning ranging and modulation. Downlink Bursts (DL bursts) of DL burst#1 to DL burst#6 are located in a (K+3)th OFDMA symbol to a (K+15)th OFDMA symbol.
In the uplink, Uplink Bursts (UL bursts) are locatable in a (K+17)th OFDMA symbol to a (K+26)th OFDMA symbol. In addition, Ranging subchannels for ranging are located in the (K+17)th OFDMA symbol to the (K+26)th OFDMA symbol.
In the data frame format used in the general communication system, a downlink frame includes a preamble field, an FCH field, a DL-MAP field, a UL-MAP field, as well as a plurality of DL burst fields.
The preamble field is used for transmitting a synchronization signal, for example, a preamble sequence, for synchronization acquisition between a transmitter and a receiver, for example, between a base station (BS) and an mobile station (MS). That is, the preamble field is a necessary part for synchronization with the data transmitted from the BS, and a modem of the MS extracts synchronization information from the preamble using various methods.
The FCH field, composed of two subchannels, transmits basic information on the subchannel, ranging and modulation. For example, by analyzing the FCH information, the MS is able to determine a size of a DL-MAP and is also able to determine the frequency reuse factor (“reuse”) used in the BS, for example, determine one of reuse1 to reuse3.
The DL-MAP field, a field for transmitting a DL-MAP message, has a variety of information for extracting data position and size in the downlink frame and for providing service to an MS. Therefore, it is possible to extract data in the frame by analyzing the DL-MAP information.
The DL burst field is used for extracting data based on the information acquired by analyzing the normal data information, for example, the DL-MAP.
The term “subchannel” as used herein refers to a channel composed of a plurality of subcarriers, and a predetermined number of subcarriers constitute one subchannel according to system conditions. One frame is composed of a plurality of, for example, 42 symbols, and one symbol can be divided into several subchannels. The symbol can be regarded as a unit time used for dividing the frame in the time domain, and a data size in one symbol differs according to format of the frame.
Next, the uplink frame in the data frame format used in the broadband communication system, as described above, is composed of a plurality of UL burst fields and a ranging subchannel field. The ranging subchannel field, a field for transmitting ranging subchannels for ranging, is used for extracting normal data information using the UL burst fields, for example, extracting data based on the information acquired by analyzing the UL-MAP.
The following data processing order is required in order to extract data from the foregoing downlink fields of the data frame according to the IEEE 802.16 standard.
1) A process of analyzing reuse information in an FCH, and FCH information for acquiring the DL-MAP size information.
2) A process of performing DL-MAP decoding to acquire a variety of information for extracting normal bursts according to information in the DL-MAP.
3) A process of extracting normal bursts based on the information acquired from the DL-MAP.
The data processing is performed in an ascending order of 1), 2) and 3), completing data reception for one frame. Commonly, a modem for the broadband communication system needs a high data rate (i.e, 10 Mbps for the downlink) and has a complex data format such as Partial Usage of the SubChannel (PUSC) and Full Usage of the SubChannel (FUSC), thus taking a very important role in data processing.
FIG. 2 is a diagram schematically illustrating a structure of an apparatus for processing data in a general broadband communication system. An 802.16-based modem is roughly divided into a received (Rx) data processor including a synchronization part, a Convolutional Turbo Code (CTC) decoder and a Convolutional Code (CC) decoder, and a transmission (Tx) data processor including Medium Access Control (MAC), a CTC encoder and a CC encoder. Referring to FIG. 2, it shows a structure of a symbol part block of the received data processor in the modem.
Referring to FIG. 2, there is schematically shown partial block structure according to the conventional art, and the partial block structure includes a channel estimator 210, a decoder 230 and a MAP decoder 250.
The channel estimator 210 estimates a channel based on a pilot in the data that underwent Fast Fourier Transform (FFT). Data compensation is achieved according to the estimated channel.
The decoder 230 operates according to the type of a CTC/CC decoder. With the use of the decoder 230, the modem corrects a data error generated during data transmission.
The MAP decoder 250 processes the FCH and DL-MAP in the frame format defined in IEEE 802.16, shown in FIG. 1. With the use of the MAP decoder 250, the modem processes the FCH and DL-MAP, and thereby extracting normal data.
The structure shown in FIG. 2, a simple structure implemented based on IEEE 802.16, has the following problems.
Data can be transmitted over one frame. In the structure of starting the next data processing after completely transmitting one data unit, when data is transmitted long along the time axis, a data rate may considerably decrease. In the structure of, after completely transmitting one data unit, estimating only the channel corresponding to the data, channel estimation performance may suffer degradation. Complex data processing is needed when various formats such as PUSC and FUSC are mixed in a frame. The structure, as it performs the next data processing after completely transmitting one data unit, needs a great number of decoders to acquire a required data rate.
According to its manufacturer, the modem can have a unique data processing structure. When the data throughput and efficiency are taken into consideration, there is a need for an effective block design.